The Flat Panel Display (hereinafter referred to as FPD) has been widely applied, because of its numerous advantages such as thin body, power saving, no radiation etc. The FPD in the prior art mainly includes Liquid Crystal Display (hereinafter referred to as LCD) and Organic Light Emitting Diode (OLED) display.
The OLED display effectuates displaying through self-luminance, thus it requires no backlight source, and the OLED display has outstanding properties such as high contrast ratio, small thickness, wide viewing angle, fast reaction speed, capability of being made into a flexible display panel, wide temperature application range, simplicity in structure and manufacturing etc., it is thus considered as a next-generation display that can replace the LCD.
OLED may be divided into two categories of Passive Matrix OLED (PMOLED) and Active Matrix OLED (AMOLED), namely, two categories of direct addressing and thin film transistor (TFT) matrix addressing. PMOLED has higher power consumption, which hinders its application in large-sized display devices, so PMOLED is usually employed in small-sized display devices. AMOLED is usually employed in high-definition large-sized display devices because of its high light emitting efficiency.
FIG. 1 is a circuit diagram of the AMOLED pixel circuit in the prior art. Within a display region of an AMOLED display device, pixels are arranged in a matrix that includes a plurality of rows and a plurality of columns, and each pixel is usually driven by a pixel circuit composed by two thin film transistors and one capacitor, that is, it is driven by adopting the 2T1C manner. Specifically, a gate of a first transistor T1 is electrically connected to a gate line Scan, a source of the first transistor T1 is electrically connected to a data signal line DATA, and a drain of the first transistor T1 is electrically connected to a gate of the second transistor T2 and one terminal of the capacitor C. A source of the second transistor T2 is electrically connected to a high voltage signal terminal VDD, and a drain of the second transistor T2 is electrically connected to an anode of an organic light emitting diode D. A cathode of the organic light emitting diode D is electrically connected to a common ground electrode VSS. In addition, one terminal of the capacitor C is electrically connected to the drain of the first transistor T1, and the other terminal of the capacitor C is electrically connected to the source of the second transistor T2. When the pixel performs displaying, the gate line Scan controls to turn on the first transistor T1, and a data signal voltage of the data signal line DATA enters the gate of the second transistor T2 and the capacitor C through the first transistor T1; thereafter, the first transistor T1 is turned off, a gate voltage of the second transistor T2 still can be maintained as the data signal voltage due to an action of the capacitor C, so that the second transistor T2 is in a turned-on state, and a driving current corresponding to the high voltage signal terminal VDD and the data signal voltage enters the organic light emitting diode D through the second transistor T2 to drive the organic light emitting diode D to emit light.
In the above AMOLED display device, the organic light emitting diode D emits light in accordance with the driving current generated by the second transistor T2 in a saturated state. Since a threshold voltage of the second transistor T2 in each pixel is different due to non-uniformity in the process of manufacturing TFT and the threshold voltage Vth of the second transistor T2 may drift in different degrees during light emission of the organic light emitting diode D, when driving is performed by adopting the 2T1C driving circuit described above, luminance uniformity of the respective pixels is poor, which may result in poor effects such as uneven displaying.